Cannabis is the most commonly used illegal drug in the UK, but what does it do to the body?
With 7.6% of adults in England and Wales saying they used it in 2018 to 2019, cannabis consumption is at a 10-year-high, according to a government report on the country's drug situation. Use was at 17% among 18 to 24-year-olds. As a Class B drug, possessing, distributing, selling or growing cannabis carries a maximum five year prison sentence, or an unlimited fine, or both.
But a 2018 law change allowed specialist doctors to legally prescribe cannabis-based medicines to patients for whom first-line treatments haven't worked. Medicinal cannabis contains the same CBD and THC compounds found in recreational cannabis, but producers must ensure the levels are consistent across batches and that batches are not contaminated.
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The chemicals in cannabis c an help with relaxation and pain relief by interacting with receptors in the body's endocannabinoid system. Some receptors in the brain are involved in emotional processing, while others are affect how pain is experienced, meaning the products can be used to treat a wide range of conditions from anxiety to epilepsy to chronic pain. It's also been found to benefit the concentration of some people with ADHD and reduce the pain of people with endometriosis, but more research into cannabis as treatment for such conditions is needed.
Although previously thought not to cause physical dependence, heavy cannabis use can rewire the brain to seek out the substance despite negative effects on users' social, family and work life. Roughly one in 10 people who use cannabis become addicted to the substance, rising to 17% for those who start using it in their teens, according to a study published in the JAMA Psychiatry journal.
According to Delamere, an addiction clinic in Northwich, Cheshire, signs of cannabis use and intoxication are:
- Fatigue, lethargy, apathy
- Dry mouth
- Bloodshot eyes
- Lack of interest in physical appearance
- Evidence of cannabis paraphernalia (e.g. joints, bongs, pipes, scales, grinders)
- Overeating (marijuana stimulates appetite)
- Obsessive engagement in activities such as gaming, music or internet whilst under the influence (users lose track of time and can spend inordinate amounts of time doing one activity)
- Impaired memory
- Slurred or delayed speech
- Unusual euphoria
- Mood swings
- Poor attention span
- Difficulty with coordination and balance
- Increased heart rate
- Anxiety, paranoia
The signs and symptoms of cannabis addiction are:
- Frequent cannabis intoxication
- Using cannabis in dangerous situations such as driving or whilst operating heavy machinery (cannabis impaires motor skills, judgment and decision making)
- Withdrawing from family and friends
- Obsessed with finding and trying different stronger strains of cannabis, or mixing with medications or other drugs for greater effect
- Paranoia, anxiety and depression
- Becoming increasingly isolated and unmotivated
- Submerging within a cannabis culture to find acceptance
- Personal relationships suffering as a result of cannabis use
- Finances, work or school suffering as a result of cannabis use
- Increased risk taking whilst under the influence
- Appearing excessively agitated and anxious if unable to get cannabis
- Severe mood swings including aggressive outbursts, extreme euphoria, apathy
- Imapired memory – perhaps a difficulty in retaining new information, remembering appointments / arrangements or repeating things over and over
- Cravings for cannabis that are overwhelming
- Ruminating past events with a disinterest in resolving issues
- Defending or justifying cannabis use despite the apparent decline in mental, physical, social or emotional health
- Disinterest in family, friends, loved ones and things once found enjoyable
- Suicidal ideation or self harm tendencies
Effects on the brain
While cannabis is known for its relaxing effects, it can make people more anxious, particularly with rising levels of THC in recent decades. For some people, it is thought to trigger or exacerbate underlying conditions like psychosis. As well as a higher risk of addiction, people who start using cannabis as teens may experience greater effects on the brain, including impaired thinking, memory and learning.
According to the US National Institute on Drug Abuse, the short-term effects of cannabis use on the brain include:
- altered senses (for example, seeing brighter colors)
- altered sense of time
- changes in mood
- impaired body movement
- difficulty with thinking and problem-solving
- impaired memory
- hallucinations (when taken in high doses)
- delusions (when taken in high doses)
- psychosis (risk is highest with regular use of high potency marijuana)
Effect on lungs
Research on whether smoking cannabis causes lung cancer remains inconclusive, but smoking the substance irritates the throat and lungs, deposits tar and chemicals in the airways, can harm lung tissue, and may increase risk of respiratory infections.
This is also the case with smoking tobacco, which cannabis is often consumed with, calling into question the myth that cannabis cancels out the harm of tobacco in a joint. One study published in the British Journal of General Practice found cannabis users self-reported more respiratory symptoms than tobacco smokers.
According to the American Lung Association, smoking cannabis injures the cell linings of large airways, possibly causing symptoms like:
- chronic cough
- phlegm production
- wheeze (a whistle or rattle sound when an airway is partially blocked)
- acute bronchitis
